The present invention relates, in general, to a fabricated gear and, more particularly, to a fabricated gear including anti-backlash mechanism. The fabricated gear of the invention may be used to replace currently used ratchet and pawl mechanisms in hand brakes for railway vehicles. The fabricated gear of the invention may also be used as a slipping clutch mechanism in an automatic set/release hand brake for a railway vehicle.
Mechanical devices which allow for one direction rotation of a shaft member are well known. These devices are typically referred to as ratchet and pawl mechanisms. A ratchet is usually a plate shaped member or wheel with slanting teeth along an outer circumference thereof. The pawl is a lever which is positioned tangential to the ratchet with one end resting on one of the teeth. When the ratchet rotates in one direction, the pawl slides over the teeth. When the ratchet rotates in the opposite direction, the pawl catches in the teeth, thus preventing rotation of the shaft member in this opposite direction. A well known use for a ratchet and pawl mechanism is in a hand brake for a railway vehicle.
As is generally well known in the railway industry, when railway cars are taken out of a train and parked at a siding or yard, the hand brake or parking brake on at least some of these cars is applied as a precaution against unwanted or unexpected movement of the cars. A typical railway car hand brake system as disclosed in U.S. Pat. No. 4,368,648 and as shown in FIG. 8, normally consists of an apparatus for manually applying and biasing one or more brake shoes against the tread of one or more wheels of the railway car be either turning a hand wheel 4 or pumping a ratchet handle on a hand brake mechanism attached to the railway car.
The hand brake mechanism is usually either a cast or stamped metal gear housing/back plate assembly which is attached to an outside end wall of the railway car. A rotatable chain drum 10 is provided therein which can be rotated by turning hand wheel 4. This rotation is transmitted directly through a drive shaft 5, a pinion 8, a gear 9, and a chain drum 10 to wind a brake chain 17 onto the chain drum 10. The other end of the brake chain normally extends through the bottom of the gear housing and is interconnected with cable or other linkage to the brake rigging (not shown) so as to draw the interconnected brake shoes against the tread surfaces of adjacent railway car wheels and, accordingly, apply the hand brake as intended.
When resistance is offered by the chain 17 to further rotation of the hand wheel 4, such resistance, acting back through the drum 10, the gear 9, and pinion 8, causes a nut to move against a ratchet member 27 which is clamped between respective friction surfaces on the nut and on the drive shaft 5, thus causing the drive shaft 5, ratchet 27, and the nut to rotate as a unit. A pawl 34 prevents rotation of the ratchet 27 in the opposite direction. The hand wheel torque is increased until a state of static equilibrium is reached, or at a point at which the brakes are fully applied, whereupon rotation of the hand wheel 4 is terminated, and the clamped ratchet 27, by means of the holding pawl 34, prevents the chain 17 from unwinding.
A gradual release of the brakes may be performed by rotating the hand wheel 4 in an opposite direction, such as in a counterclockwise direction, which partially loosens the nut to reduce the clamping force on the ratchet 27. This action allows the pinion 8 and gear 9 to rotate to reduce chain load and release the brakes.
Alternatively, a quick release of the brakes may be performed by rotating a quick release handle 32 in a clockwise direction. Generally these quick release mechanisms include a releasable connecting means between the hand wheel shaft and the gear train. When the connecting means is released, the gears of the gear train rotate rapidly, without constraint by the pawl and ratchet wheel, but the hand wheel remains stationary.
Typically gears such as those used in ratchet and pawl systems are formed from a casting process. During this process, care must be taken in order to ensure that proper tolerances are met and a significant amount of machining is often required. Additionally, trapping of any impurities within the casting must be avoided as such could cause the gear to break. Thus, there is a need in the art for a fabricated gear which can overcome the aforementioned disadvantages of a cast gear. There is also a need in the art for a fabricated gear having an anti-backlash mechanism which may be used as a replacement for currently used pawl and ratchet mechanisms in hand brake assemblies.
The fabricated gear having an anti-backlash mechanism of the present invention has been disclosed as one of the components of an automatic set/release hand brake for a railway vehicle in co-pending application Ser. No. 09/507,227, entitled xe2x80x9cAutomatic Application Hand Brakexe2x80x9d. The disclosure of this application is hereby incorporated by reference thereto. This co-pending application was filed by the assignee of the present invention. In this co-pending application, the particulars of the fabricated gear having the anti-backlash mechanism were not disclosed nor were they claimed.
Briefly, the fabricated gear of the invention comprises a plurality of plates disposed in series one on top of another. Each of the plates include a plurality of teeth along an outer circumference thereof. An aperture extending through a center portion of each of the plates is provided. This aperture forms an inner circumference within each of the plates and is capable of receiving a shaft member therethrough. A means for securing said plates together is provided so as to form the fabricated gear. This fabricated gear may be keyed onto a shaft member.
Alternatively, an anti-backlash mechanism may be provided in the fabricated gear to achieve one direction rotation of a shaft member. This anti-backlash mechanism is formed by providing at least one indentation within an inner circumference of at least some of the plates. This inner circumference in the plates is formed by the aperture extending through the plates. This at least one indentation is capable of forming an opening between the inner circumference of the plate and an outer surface of the shaft member. A cylindrical member is provided which is capable of interacting with the at least one opening to cause the plates to lock up onto the shaft member upon the application of a force in a first direction and to freely rotate with respect to the shaft member upon the application of a force in a second direction.
It is, therefore, a primary object of the invention to produce a fabricated gear that is economically manufactured and operates in a simple manner.
It is another object to produce a fabricated gear which overcomes the disadvantages of cast gears which require extensive machining to achieve close tolerances.
It is still a further object to produce a fabricated gear which is stronger than cast gears.
It is yet another object to provide a fabricated gear having an anti-backlash mechanism which may be used to replace currently used ratchet and pawl mechanisms.
It is still yet another object to provide a fabricated gear having an anti-backlash mechanism which may be used as a slipping clutch mechanism within an automatic set/release hand brake for a railway vehicle.
In addition to the several objects and advantages of the present invention generally described above, various other objects and advantages of the invention will become much more readily apparent to those persons who are skilled in the relevant art from the following more detailed description, particularly, when such detailed description is taken in conjunction with the attached drawing figures and the claims appended hereto.